Cortisol Test Might Detect Horses at Higher Risk for Colic

By testing cortisol circadian rhythm ratios (CCR) in the bloodstream, researchers found that horses with CCR ratios below 0.30 were 2.3 to 3.1 times more likely to suffer a colic episode than those with normal CCR ratios.

Photo: Anne M. Eberhardt/The Horse

Preventing colic often is easier than dealing with it. But how can you tell if your horse is at risk for colicking and, thus, make necessary adjustments to his life to reduce his colic risk? A group of Brazilian researchers recently proposed that a fairly simple method, known as cortisol circadian rhythm (CCR) ratio, could be used to identify horses under chronic stress, which could indicate a higher likelihood of colic.

Rafael Faleiros, DVM, PhD, a professor at Federal University of Minas Gerais and author on the study, explained that the CCR ratio is a "simple method proposed by Dr. Robert Douglas (PhD) from BET Laboratories to assess the CCR," involving two blood samples taken eight hours apart. Cortisol, which is primarily produced by the adrenal gland, is often termed the "stress hormone" because its levels rise in response to stress in horses and other species.

"A CCR ratio below 0.30 indicates that there is an abnormal stimulus to the production of cortisol," Faleiros explained.

In the study, researchers separated 116 police horses into four groups according to their housing conditions and type of work:

Group 1 was stabled full-time and used for urban patrol;

Group 2 was stabled full-time and used for sport activities;

Group 3 was stabled part-time and used for urban patrol; and

Group 4 was kept on pasture full-time with no structured activity.

Researchers took blood samples from each horse between 6:00 and 7:00 a.m., and again eight hours later to determine the CCR ratio. Additionally, the incidence of colic among all groups was examined over the course of a year, beginning six months prior and continuing six months after the blood sample collection, which took place in a single day.

During the one-year study period 107 colic cases were reported among all four groups of horses. Upon reviewing the results of their investigation, the researchers found that:

Group 4 (full-time pasture) had the highest (most normal) CCR ratios and made up the smallest percentage (12.1%) of total colic cases;

Groups 1, 2, and 3 had lower (more abnormal) CCR ratios than group 4, but there was not a notable difference among the average CCR ratios of these three groups; and

Horses with CCR ratios below 0.30 were 2.3 to 3.1 times more likely to suffer a colic episode than those with normal CCR ratios.

Previous studies have linked stressful conditions, such as limiting pasture access and intense exercise, with colic, and this study confirmed the association. "We speculate that CCR ratio determination can be a simple and useful technique to detect horses at risk of colic," the team concluded.

The study, "Cortisol Circadian Rhythm Ratio: A Simple Method to Detect Stressed Horses at Higher Risk of Colic?" was published In April 2011 in the Journal of Equine Veterinary Science. The abstract can be viewed online.

About the Author

Casie Bazay holds a bachelor of science degree in education from Oklahoma State University. She taught middle school for ten years, but now is a nationally certified equine acupressure practitioner and freelance writer. She has owned Quarter Horses nearly her entire life and has participated in a variety of horse events including Western and English pleasure, trail riding, and speed events. She was a competitive barrel racer for many years and hopes to pursue the sport again soon.

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